Many of electronic devices having information processing functions, typified by a personal computer and the like, include electronic components, such as a CPU, which produce heat while executing processes. The electronic component itself such as a CPU is a heat-producing element and may cause malfunction when a temperature thereof is excessively increased. Thus, generally, most of the electronic devices such as personal computers are internally equipped with some kind of means for cooling an electronic component such as a CPU. As one of such cooling units, there is known a cooling unit for cooling a heat-producing element by means of a coolant (see, for example, Japanese Laid-open Patent Publication No. 2005-11928).
Many of electronic devices such as a personal computer are provided with, in addition to a CPU, other types of electronic components that produce heat while executing processes, such as a chipset for controlling data communications in a CPU and a memory. In recent years, due to an increase in processing capacity of electronic devices such as personal computers, heat-producing components other than a CPU have been already well on their ways to becoming hard to ignore. For this reason, there is proposed a technique for cooling two or more heat-producing elements by means of a cooling unit employing a coolant like the one mentioned above (see, for example, Japanese Laid-open Patent Publication No. 2007-27340).
The cooling unit that cools two or more heat-producing elements using a coolant as mentioned above is provided with: two or more heat absorbing sections that allow the coolant running inside to absorb heat; a heat radiating section that radiates the heat accumulated in the coolant to the outside; and a pump or the like that causes the coolant to flow. In this type of cooling unit, there is formed a path that links the heat absorbing sections, the heat radiating section and the pump.
Conventionally, in many of ordinary cooling units using a coolant, the coolant in a state of having the lowest temperature upon leaving a heat radiating section is first made to flow to a heat absorbing section that absorbs heat produced by a heat-producing element with the highest heating value such as a CPU. Meanwhile, in many of pumps used for circulating a coolant, an upper limit below which circulation of the coolant is allowed is set to the temperature of the coolant in view of resistance to heat. Lately however, since the heating value has been greatly increased due to an increase in the processing speed of a CPU or the like, there is a high possibility that the temperature of the coolant may exceed the upper limit set in the pump, as a result of being warmed by heat produced by the CPU. To this end, conventionally, the coolant upon leaving a heat radiating section is first made to pass through a heat absorbing section to absorb heat produced by a CPU or the like, and then temporarily cooled before sent to a pump to lower the temperature that has been increased as a result of absorbing the heat from the CPU. This requires a complicated path, which not only makes it difficult to mount a cooling unit on an electronic device, but also reduces cooling efficiency in the cooling unit because the path needs to be long.